Separating solids from a liquid



Dec. 27, 1949 A. M. KlvARi ETAL SEPARATING SOLIDS FROM A LIQUID Filed July 10, v1948 Wsw: +525 Patented Dec. 27, 1949 UNITED ssnna'rmc soups non A mourn Animar. mm1 and Esi-1M. xeuy, L. met, caux.

Application July 10, 1948,'Serlal No. 38.063

4 Claims.

This invention relates to improvements in separating solids from a liquid.

If a liquid containing solids suspended therein, other than particles in true colloidal suspension, is held in a quiescent state for a suillciently long period of time, the solids settle and the clear liquid can be drawn oi. Such an. operation requires a considerable period of time; when the volume of liquid to be handled in a given time period is relatively large, the size of the equipment required will be inordinately large. To the end that the size of the equipment can be reduced and the rate of settling increased, various schemes and proposals have been advanced. The present invention is concerned with an improved process which is particularly suitedl to the clarification of a liquid such as water containing solid waste such as sewage or industrial waste waters. Such a liquid may contain solids in various sizes as well as solid organic matter having aA biological oxygen demand (frequently abbreviated as B. O. D.) and dissolved organic matter. To render the liquid useful or capable of release it mustgbe freed of solids, odors, and of organic matter so that it is stable, clear and remains so upon release;

The process of this invention includes the utilization of repeated aeration,v agitation and sedimentation of the solid and dissolved organic matter present in the liquid to the end that the latter is clarified, its B. O. D. is'completely satisiled and the liquid is clearA and stable. process Awill become further apparent'upon a brief description of a preferred operation and of apparatus which can be employed to practise the invention. Briefly, such apparatus may include two units which are operated in series and each of which includes a `relatively large bodyof liquid which is caused to flow through a tank or vessel having, in the preferred practise of the invention, three concentrically arranged compartments, an outer s edimentation compartment, an intermediate agitation compartment, and a central treatment compartment into which (1) a portion of the liquid and coagulatedaerated solids from the agitation compartment is admitted together with (2) fresh incoming liquid, the fresh liquid inthe central treatment zone being mixed with that from the agitation compartment containing a larger concentration of solids; Solids settling in the iirst tank or vessel 'are removed for disposal while the eilluent liquid resulting from the first aeration-occulation-sedimentation operation is then subjected to a substantially similar treatment to remove remaining colloidal and dissolved organic matter Vand to provide a final eiiiuent of relatively great clarity which is free of any objectionable odor and scum and substantially free of yany solid matter. In this way, we are enabled to treat, for example, an industrial waste having an extremely high biological oxygen demand and which otherwise provides odor, and scum problems. Obviously, the process can be applied to less severe sewage and industrial wastes with equal success.

Wel have further found that the operation in the rst liquid body is facilitated ii a portion of the sludge resulting from the treatment of the second liquid body is returned and is mixed with incoming eilluent and is then subjected to treatment in the first liquid body; In this manner, the overall use of air is reduced while the settling rate of solids in the' first oxidation-ilocculation-sedimentation treatment zone is lncreased; apparently, the solids which settle from the second liquid body and which have been repeatedly aerated and nally settled, have a deiinite and an increased ailinity and fico-forming ability for like waste materials so that these assist inl effecting coagulation, ilocculation, and sedimentation.

In the case of liquids such as raw sewage having a biological oxygen demand, air is pref'- TheVr erably admitted to each central compartment or treatment zone to assist in mixing and circulating the liquid therein, to freshen the liquid, reduce odors and scum and lto satisfy vthe biological oxygen demand. In addition, the aeration of the uid enables organic solids to be held in the tank for a period of far beyond that normally possible without encountering troublesome decomposition.

Sludge collection means may be provided in the agitation compartment to receive a sludge which separates out in that compartment and return this for re-introduction and mixing with the incoming uid. In this way, maximum size particles are built up, these settling quite rapidly.

This also enables an improved utilization, as will be described, to be made of any chemical added for treatment` such as ferric chloride or other treatment agents. Mixing of at least a portion -oi' a finely separated sludge with the incoming or raw ellluent liquid containing additional solid particles results in an increase in the settling rate to the end that clarified liquid can be drawn off at a maximum rate per unit of vessel area or volume. Further, the return of at least a portion of the final sludge to an aeration zone 3 results in an increase in the aeration enacted in the sludge so that an aerobic sludge is built up and maintained.

It is an object of the present invention to provide an improved process for removal of solids and other objectionable components from a liquid such as sewage or an industrial waste.

The invention includes other features and objects of advantage, some of which, together with the foregoing, will appear hereinafter.

In the drawing, the single gure is a diagrammatic representation of suitable apparatus which can be employed and a flow sheet.

Referring to the drawing, we have indicated two substantially like units 46 and 41 and each of which includes a tank I having a wall 52 with an eilluent trough 53 formed upon an upper portion of the wall. Each tank includes a. bottom 54 sloping inwardly toward its center and including a sludge discharge pocket 56 and an inlet line 51 for the discharge of liquid to be treated. One or more beams 58 are extended across the tank to provide a support for a bearing 59 on which center column 6I is mounted for rotation. An

annular wall 12 is supported from the transverse beams 58 above the tank bottom by several brackets 13, the wall separating the sedimentation compartment and the agitation compartment.

The central column Bi includes a gear 62 at its upper end which rests upon the bearing 59, the gear being enmeshed with-a gear 63 driven by a prime mover generally indicated by numeral 84. At its lower end, the column is fitted into a seal 6U in theinlet pipe 5l.

liquid as it rises through the column 6i. A diffuser 61 is provided in the column being supplied with air through line 68 from an air blower 69, The aerated sludge-influent liquid issues from ports 1i' adjacent the upper portion of the liquid level in the tank, and causes agitation in the upper portion of the so-called agitation compartment, the region below this upper portion being one in which settlement occurs.

Mounted upon the central column for rotation with the column are a plurality of radial rakes 14, the rakes being supported upon the column at 16 and by braces 11. The rakes move the sludge toward the sludge pocket while that which is in suspension adjacent the ports 66 enters these t0 mix with the fresh liquid.

The mixing operation effected in each mixing zone in the central columnbetween the fresh liquid and solids and the settled solids is effective to provide a zone of relatively high sludge concentration in the agitation compartment so that the sludge in the agitation compartment has a tendency to settle rapidly. That sludge which enters the sedimentation compartment has a relatively rapid settling rate so that the rate of liquid ow through the clarifier is relatively high and so that the final effluent liquid is clear and well aerated. If desired, a scum skimmer can be provided to remove any material which finds its way to the surface of the liquid in either or both In operation, on a iluid such as raw sewage l admitted to the treatment zone provided by solids, the fresh :fluid is aerated and the solids The central column includes inlet ports 56 at its lower end so .that sludge from the agitation compartment can be admitted to the influent liquid to mix with the Cil quickly become aerobic and any B. 0. D. is satisiled more readily and more completely.

. To eifect this, at least a portion of the sludge which passes through the sludge outlet li in tank 41 is withdrawn by pipe 83 and is returned to the influent line 51 on the rst unit to mix with influent raw waste. The sludge return through pipe 83 can be continuous or intermittent depending upon the operation desired and upon the quantity of sludge produced. For example, if the sludge production is very heavy during certain periods, then some of the sludge canbe taken oi! line 83 to line 84 and sent to a sludge concentrator 86 along with the sludge derived from the iirst unit 48. Liquid from thev sludge concentrator Il is returned to line 81 to the inlet to the rst unit 46 through line 81.

It desired, asuitable coagulant such as ferrie sulphate or iron containing salts such as ferrie chloride, alum, chlorinated copperas or other suitable coagulant can be added to line 8| from a suitable feeder device through line 88.

hours of. sedimentation in the outer compartment and where an air addition amounting to 0.15 cfm. per gallon is applied to each, we will obtain an over-all removal of suspended solids and a reduction in B. O. D. amounting to approximately This can be increased by allowing longer detention periods in the mixing compartment of each unit. likewise increased removals are ob'- tainable through the use of a coagulant, pref' erably an iron compound applied to the liquid to be treated just ahead of the secondary body of liquid.

The use of air, together with the internal aeration and recirculation with partially conditioned precipitated solids brings about an acceleration of the normal lpuriiication process, making pos; sible a degree of treatment which is ordinarily not obtainable except in complete treatment plants using trickling lters or activated sludge. The process of this invention enables a complete treatment of sewage and industrial wastes to be effected at a cost approximately half that otherwise necessary if ordinary complete treatment processes were employed.

Operating results in a packing house waste are as follows:

Total Sus nded SW1P sonas srids l Fat PH Raw Waste 5 350 3, 970 266 7.2 Primary Eiuent. 200 l2 7. 3 Secondary Effluent. 200 6 7. 65 Do 200 4 7.65

and suspended solids in which the liquid is passed consecutively through first and second pools in which settlement of solids takes place to form sludge of downwardly increasing density and claried liquid of upwardly increasing clarity,

relatively dense sludge being removed from the lower portions of each pool, the improvement which comprises introducing previously settled sludge from the ilrst pool into the incoming mixture, aerating the resultingmass, introducing the aerated mass into a| zone in the nrst pool in which settlement of some of the solids occurs with resultant production of a partially claried liquid, passing the partially clarified liquid into a second zone in the pool in which further settlement and clarification occurs to produce a second partially clarified liquid, introducing said second partially claried liquid into the second pool, introducing settled sludge from the second pool into said second partially clarified liquid, aerating the result'- 3. Process according to claim 1 in which a.

coagulant is introduced into the second partially claried liquid prior to introducing this liquid into the second pool.

4. Process according to claim 1 in which sludge settled out in the second pool. is introduced into the incoming mixture to the irst pool and aerated therewith and a. coagulant is 'introduced into the second partially clarified liquid prior to introducing it into the second pool.

EARL' M. KELLY.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,217,143 Stevenson Oct. 8, 1940 2,223,257 Mallory NOV. 26, 1940 2,233,792 Mallory Mar. 4, 1941 2,324,400 Kelly et al. July 13, 1943 4v2,425,065 Kivarl Aug. 5, 1947 .2,444,671 Prager- July 6, 1948 2,446,655 Lawrason Aug. 10, 1948 

